Yes, all of you be submissive to one another, and be clothed with humility.”
-1 PETER 5:5
If our desire is for maturity, that is, if we desire to come to the full-knowledge of Christ and grow up into Him in all things, we should naturally pay attention to those who are elder in the Lord. My elder brother, or my elder sister, has walked with the Lord longer than I have. The implication is that they are more conformed to the image of Christ than myself; they have experienced a deeper work of the Cross than I have; thus, they have more practical wisdom than I do, they have something to teach me, and I need to hear Christ in them so I, too, can grow.
It should be obvious to you who is, and who is not, your elder in the Lord. And, it should be plain to see that not everyone who is older is necessarily elder. If you say you are a believer but you live no differently from the world, then you can be as old as Methuselah yet you are certainly not an elder.